Yep you got the plug effects backwards. Both ports open will give you a stronger SPL but the sub wont go as low. Ive always ran my pair with the plug in one port on both subs as obviously a pair of VTF2 MK3 is plenty of SPL for my 17x20 room. Unless I was dropping this sub in a large room...
Remember that a good sub is for life. Regardless of what speakers you may go with, now or in the future, your sub will be there to provide the frequencies that your speakers won't efficiently produce with the same SPL. A larger amp, like in the Outlaw, will give greater headroom and serve...